The present invention relates to a night vision system for detecting objects at relatively low visible light levels. In particular, the invention concerns an active night vision system having an anti-blinding scheme employing pulsed illumination and synchronization with detected pulsed light sources from oncoming vehicles.
Night vision systems are utilized to allow a user to see objects at relatively low visibility light levels. Night vision systems typically are classified as either passive night vision systems or active night vision systems. In known passive night vision systems used in automotive applications, mid-infrared cameras are used to image objects using the ambient infrared light emitted by the objects in the environment. Mid-infrared night vision systems have relatively few pixels and, accordingly, images formed using such cameras have low video resolution and a relatively narrow field of view. Known active night vision systems utilize a near-infrared (NIR) laser diode or a filtered incandescent light source to generate NIR light. The NIR light is subsequently reflected off objects in the environment and is received by a NIR-sensitive camera. The camera generates a video signal responsive to received light.
An improved active night vision system is disclosed in U.S. patent application Ser. No. 09/598,484 entitled xe2x80x9cA Night Vision System Utilizing A Diode Laser Illumination Module And A Method Related Thereto,xe2x80x9d which is herein incorporated by reference. That application describes an active night vision system that uses a NIR diode laser to illuminate the region forward of the vehicle, and a CCD camera to process and display images within the illuminated region. Because NIR light is invisible to the human eye, the laser light can be formed into a high beam pattern to illuminate potential hazards without blinding oncoming vehicle operators. Such systems, however, are susceptible to blinding by oncoming vehicles similarly equipped with a night vision NIR light source.
One solution to night vision system blinding by oncoming vehicles similarly equipped with a NIR light source is provided in U.S. patent application Ser. No. 09/683,840 entitled xe2x80x9cGPS-Based Anti-Blinding System For Active Night Vision.xe2x80x9d In that application, GPS is used to determine the direction of travel of the vehicles as well as an absolute time reference. Vehicles proximate one another synchronize their pulsed light sources to the absolute time reference signal with the phase of the light pulse based on the direction of motion of the respective vehicles. In this way, two cars approaching one another from opposite directions will have their NIR light sources pulsed out-of-phase with each other at duty cycles below 50% to avoid having their light source xe2x80x9conxe2x80x9d when the opposing vehicle""s camera is also xe2x80x9con.xe2x80x9d The disclosed anti-blinding scheme, however, requires that all night vision equipped vehicles must also be equipped with GPS systems.
Thus, there exists a need for alternate night vision systems and methods related thereto that mitigate or eliminate blinding of the vehicle""s night vision system by similarly equipped approaching vehicles.
The present invention provides an active night vision system and method related thereto which mitigates the blinding effects of nearby similarly equipped vehicles. The anti-blinding scheme of the present invention synchronizes the pulsed light sources of respective vehicles approaching each other from opposite directions to be out-of-phase without the use of GPS or any other external reference source. A night vision system in accordance with one embodiment of the present invention includes an illuminating device such as a NIR light source and beam-forming optics for illuminating a region in the forward direction of travel of the vehicle. A receiver, such as a camera, receives light reflected off objects in the illuminated region and generates a video signal responsive to the received light. A light sensor, such as a photodiode, generates a light intensity signal in response to detecting light at approximately the same wavelength as light emitted by the pulsed light source. The controller is adapted to receive the light intensity signal during first and second time periods between pulses of the light source. The light intensity signals are compared during the first and second time periods, and the light source pulse timing is modified in response to a difference in the respective light intensity levels during the first and second time periods. The difference in light intensity levels during the respective time periods indicates that another source of light at approximately the same wavelength as the pulsed light source is present, but is not exactly in-phase or out-of-phase with the reference vehicle""s pulsed light source. Thus, the timing of the pulsed light source is modified such that the light intensity levels during the inactive period are substantially constant. This is indicative of the oncoming vehicle""s pulsed light source being exactly out-of-phase with the present vehicle""s pulsed light source.
Other advantages and features of the invention will become apparent to one of skill in the art upon reading the following detailed description with reference to the drawings illustrating features of the invention by way of example.